1. Field of the Invention
The present invention generally relates to a method and apparatus for the assembly of body components to an automotive body that has undergone a progressive series of positioning and welding steps so as to produce a structurally rigid body frame, termed a body-in-white. More specifically, this invention relates to reestablishing a new grid system (XYZ coordinate system) for a body-in-white, after assembly, so as to direct the associated tooling to establish net attachment positions for all body components thereby eliminating the B′L, B′R, C′L, C′R need for any slip plane adjustment techniques.
2. Description of the Related Art
For many decades, automobile and truck body frames, that typically include at least an underbody, a pair of side frames, and front and rear headers, conventionally undergo a progressive series of positioning and welding steps before a structurally rigid body frame, termed a body-in-white, is produced. Though bodies are still manually assembled and welded, emphasis on automated assembly and welding operations has for many years generated numerous automated and semi-automated framing systems.
In an attempt to create and maintain dimensional integrity in the building of automotive bodies, typically, framing systems that involve a degree of automation include the operations of locating the components relative to each other on the underbody. Primary locating points established on the underbody are used throughout the body shop operation as well as in the body inspection room and are generally established by locating on each of the rails, a four way locating pin forward and a two way locating pin rearward. Usually, the underbody is then clamped in place at specific points of location. The primary locating points are also used to locate for purposes of inspection in the body build shop. The components are located relative to each other and relative to the underbody and are loosely assembled to each other. Typically, the various components include a floor panel, right and left body side panels, a dash panel and either a roof panel or transversely extending header members upon which a roof panel is subsequently mounted. After these individual panels are stamped, in some applications, preliminary assembly operations are performed on individual panels as, for example, adding door hinge and latch hardware to the body side panels at approximate locations on a door opening, adding seat mounting brackets and reinforcements to the floor panel, etc.
The set of panels that constitute a subassembly of the finished vehicle body are then brought together and loosely assembled to each other. This initial loose assembly technique is frequently accomplished by a so called “toy tab” arrangement in which one panel is created with a tab projecting from one edge that is received in a slot in an adjacent panel. This technique interlocks the panels and frame members to each other to the point where they will not separate from each other, but does not achieve a rigid assembly, that is, for example, the side panels may tilt slightly relative to the floor panel. Alternatively, some initial pre-tack welding may be performed in order to loosely maintain the components together. The loosely assembled subassembly is then transported to a framing/welding station whereat, in order to accurately establish the desired final geometry of all of the components of the body-in-white, the toy tab components are clamped to locating frames, often termed gate fixtures. Thereafter, welding operations, are performed within a framing and subsequent respot station to more permanently and securely weld the components together and to accurately form a rigid structure referred to as the body-in-white. Current body framing stations employ both fixed and robotic welders that can be programmed to perform several welds at different locations on the body in one framing station. The welders typically are located at opposite sides of the conveying line at the welding station, and when the body's subassembly is located in the welding station, the fixed weldings and robotic welders perform welds on designated areas on the body. In those cases where clamping frames are positioned on opposite sides of the body, clearance problems may restrict motion of the welding heads that must pass through the clamping frame before they have access to specific areas of the body to be welded. This will result in the performance of only a portion of the required welding at one station and the advancement of the partially welded subassembly to a subsequent respot welding station where different clamping frames allow the welding head to access those portions of the body assembly that could not be reached by the welding heads in the first station. After the body is transported to the final welding, or respot station, the remaining welds are made to establish a structurally rigid body frame.
Although many variations of the above process are known, it is the general object of each framing system to accurately net locate the body components relative to each other and maintain the established net location or position throughout the later welding operations, until the structural rigidity of the body-in-white is sufficient to preserve the desired geometric configuration throughout the assembly process.
It is readily recognized that these conventional assembly techniques include many assembly steps that require parts to be physically stacked on top of one another and then secured to each other by welding, and wherein each component is created with a certain accuracy and tolerance limits. That is, a particular component, and any point on that component, is typically required to be manufactured to a specific dimensional configuration, within a specified tolerance range. If an individual panel to be affixed references a point on another panel, the reference point also has a dimensional tolerance variation. The tolerance of the assembly formed by these components will also be “stacked” together. That is, the dimensional tolerance of the first panel will be added, to some degree, to that of the second panel to be attached thereto. As more components are fixed to the assembly that references additional attachment points, the tolerances of the individual points are “stacked” to create a greater tolerance variation for the “stacked” components.
The small tolerance variations in the primary locating points for locating the underbody combined with the gate fixtures that typically allow some play in the positioning of the panels prior to clamping inherently results in some built-up inaccuracies for the body-in-white. Also, the repositioning of the framing system in a respot station, again, results in an additional positional tolerance variation inherently creating additional inaccuracies for the location of the various panels with respect to each other. Accordingly, it is quite evident that as a number of panels with positional dimensional tolerances are stacked the total manufacturing tolerance of the framed body-in-white will increase. Experience has shown that the “stacking” built-in tolerances in the framing process increases the total manufacturing tolerance and can become quite substantial.
Accordingly, over a period of years, many have attempted to improve the manufacturing method so as to reduce the overall or total tolerance in vehicle assemblies utilizing a variety of techniques in an attempt to reduce the inherent inaccuracies of the vehicle body assembly as well as the body-in-white.
To attempt to reduce the inherent built-in inaccuracies in the process of building automobile bodies with the objective of reducing overall tolerance variations, many alternative framing schemes have been proposed over the years. For example, DeRees, U.S. Pat. No. 5,090,105, teaches a modular vehicle construction assembly method in which various structural modules are fabricated and assembled with operating vehicle components prior to mounting with other fabricated and assembled modules. For example, a first module having a chassis frame and a passenger platform that is used in the formation of the underbody of the vehicle is proposed. A second module in the form of a cowl or dashboard includes a structural frame, preferably formed from stamped panel components that include a windshield frame portion integrally formed with a dash panel frame portion. A third modular component includes a flooring platform, two first side-wall structures and at least one closure device extending across the first sidewall structures above or at one end of the flooring system. The fourth module includes two second sidewall structures, reinforcement for supporting the second sidewall structures in a fixed position with respect to each other, a hood panel and device for displaceably mounting at least a portion of the fourth module to the first module. Each of the first through fourth modules is completely assembled, including the installation of vehicle operating components, prior to its attachment to the other modules. The resulting structure incorporates each of the modules by locating each module at a net position thereby reducing the overall built up tolerance for the complete assembly. However, within each module, DeRees is still proposing that the device for securing the panels together utilizes conventional welding techniques or welding substitutes such as mechanical interlocking of the panels, mechanical fastening, bonding with adhesives, bolting, riveting or the like.
Angel, U.S. Pat. No. 6,378,186, teaches a framing device for assembling and welding a body-in-white utilizing completely separate framing and welding operations that are typically intermixed in conventional framing systems. The framing device is a unitary frame structure within which an underbody, side frames, and other body components can each be supported and accurately positioned with respect to each other prior to the welding operation. Using an appropriate number of clamping devices, the net position of the body components that constitute the body-in-white are properly established and maintained, such that gate fixtures are unnecessary during the welding operation. The structure of the framing device provides considerable access to the body-in-white supported within the interior of the framing device such that a greater number of welding guns can be used during the welding process to complete all of the welding necessary to maintain the rigidity and geometry of the body-in-white in a single welding operation or station.
Bonnett et al., U.S. Pat. No. 5,845,387, teach a method of constructing a vehicle body with reference to a single assembly station by moving multiple panels into an assembled position nonclampingly fixed with an adhesive and in spaced relationship without direct contact therebetween. The vehicle body is constructed by presenting a plurality of discrete body panels into assembled positions with respect to a single base for application of an adhesive thereon to fix the body panels in a nonclamping, spaced relationship without direct contact therebetween. The body panels include an underbody, a first side panel on a first side of the underbody and a second side panel on a second side of the underbody, a front end member mated with the underbody, the first side panel and the second side panel, and a roof panel substantially co-planar with the underbody in mating relationship with upper mating flanges on the first and second side panels. Such structure avoids tolerance stack-up between the assembled panels by controlling the adhesive bond gap variance between the panels. The adhesive is a heavy-duty urethane structural adhesive. The resulting vehicle body assembly reduces tolerance stack-up and has the additional advantage of having relatively little inherent stress points developed between mating panels since they are assembled at a single stage framing fixture, or assembly apparatus.
Oatridge et al., U.S. Pat. No. 6,360,421, like DeRees, teach a manufacturing or assembly technique wherein the assembly includes a plurality of individual components that are independently formed into a substantially rigid initial subassembly structure thereafter, for each remaining component referencing from the substantially rigid structure a desired position for each remaining component and fixing such remaining component to the subassembly at the desired position whereby the overall tolerance of the manufactured assembly is reduced.
Although a majority of the prior art has recognized the existence of built in inaccuracies in the building of automotive bodies, by the stacking of tolerances between adjacent components, resulting in unacceptable mating conditions, little has been said in the prior art regarding those inherent inaccuracies of the various processes themselves. For example, many of the processing techniques require the rigid clamping of the various components, panels or subassemblies on the fixtures for the purpose of obtaining maximum support rigidity before the components are welded together. However, if any misalignment exists between associated components or panels, the spot welding that creates the weld will tend to displace the component or panel from the desired assembly location to some unknown position relative to design-intent or an established X, Y and Z Cartesian coordinate system. Accordingly, although modular construction may be suggested to avoid tolerance build up, the clamping of the modular components into the rigid fixtures can easily result in stretching or compression points in the vehicle body that may cause stress induced cracks or other deficiencies especially after the weld is created. Thus, the problem with existing fixtures whether they are framing fixtures or tooling to assemble modular components is that these assemblies are assembled with internal stresses that can cause deformities in the assembled sheet metal resulting in failures to the assemblies when in use, i.e. popped welds, etc. Further, after clamping these components or panels into the rigid fixtures, thousands of welds are produced resulting in additional stresses as well as distortion due to the heat and pressure associated with the use of welding guns leading to the conclusion that after the body-in-white has been processed in the appropriate framing and welding stations, it is impossible to know the final location of the surfaces as well as any targets, master holes or whatever else is attached to the panels before the welding operations occur. Although the objective in the framing and welding station is to locate panels at so called “net” or design-intent locations, the variety of unknowns due to processing through the stations causes every vehicle body and its associated surfaces to be built differently. In the past, this has been considered to be an acceptable body to process providing that master attachment points or panels are within an acceptable tolerance range from net or design-intent location. For decades, it has been common practice in the automobile industry to incorporate a “slip plane” in the assembly of outer body panels to the body-in-white. The slip plane enables the appropriate outer panels to be attached and manually fit at assembly relative to adjacent panels. Until recently, a slip plane was necessary in order to meet quality and fit requirements of the marketplace and competition, and to provide an appearance that is more pleasing and more aerodynamic due to flushness and/or alignment of features on an outer panel with adjacent outer surfaces of a vehicle.
Slip planes are designed in component assemblies where as a result of manufacturing variations of the components, as for example a door and a hinge on a vehicle, it is necessary to provide a device to enable a door to be manually fit to the body opening at final assembly. The slip plane permits fore/aft and up/down adjustment of the hinge as necessary to permit the door to be fitted within the body opening with an equidistance gap around the door and between body openings. Slip planes can be planned to be within any coordinate or plane of an X, Y and Z coordinate system as for example on a vehicle the fore/aft direction, cross-car direction and up/down direction that are respectively designated as X, Y and Z. The appropriate plane to incorporate a slip plane is based on the specific surface feature required to be aligned with respect to an adjacent surface feature on an adjacent outer panel of the vehicle body. The slip plane is an adjustment feature that compensates for the inevitable tolerance variations that differs between vehicles. Slip planes are generally used at the interface between attachment points as for example a door hinge and the major trim panels to which the hinge is to be attached to the vehicle body. Because of the tolerance variations of the body-in-white, excessive gapping may result between panels or between the door and a door opening. Further, in the case of moving trim panels such as doors, and decklids, pinch points may occur as a result of variation in location of the attachment point with respect to the opening in which the major panel is mounted. Accordingly, a slip plane, as for example in the door hinge and/or door panel, has always been used to provide for manual final fitting of the door with respect to the door opening to balance out the gap between the doors and major trim panels, such as fenders, as well as to ensure proper flushness of adjacent major outer panels.
The problem of inherent stresses and distortions as a result of the assembly process has been recognized in the prior art and several attempts to provide more accuracy in the assembly process of a vehicle have been made in order to solve the problem.
Earlier, it was believed that by establishing the attachment points at net or design-intent position on the body-in-white frame structure at least some of the inaccuracies between the panel to be attached and the body-in-white would be eliminated. However, due to the distortions of the body-in-white as a result of the assembly/welding processes, it was still necessary to provide a slip plane in order to permanently attach the outer body attachment panels for the purpose of obtaining proper gaps and correct flushness between adjacent panels as well as alignment of feature lines between adjacent panels. The apparatus and process by which a device established a datum position from an object having dimensional variations within a known tolerance range is disclosed in U.S. Pat. No. 4,976,026 to Dacey, Jr. and is owned by the current assignee hereof. Dacey, Jr. teaches an apparatus and method for establishing a location in space (a datum position) utilizing an object having dimensional variations in each of the X, Y and Z planes within a known tolerance range. Upon establishing a location in space, the device is immobilized at the datum position and work is performed on the body-in-white with respect to the datum position. The apparatus includes a fixed base structure for rigid mounting to a floor adjacent to an assembly line, a transfer platform moveably attached to the base structure so that the transfer platform can move in a horizontal direction with respect to the fixed base structure, a support structure assembly attached to the transfer platform that is adapted to move in a horizontal direction perpendicular to the direction of movement of the transfer platform, a vertical slide assembly moveably attached to the support structure assembly and moveable therewith in a vertical direction, fluid actuated positioning and locating members attached to the apparatus for immobilizing the horizontal and vertical movements of the apparatus, as well as a plurality of probes attached to the apparatus for locating pre-established selected reference surfaces or gage points from which the datum position can be established. The invention further includes a work performing tool attached to the position finding apparatus so that it can perform work on the object with respect to the established datum position. Since the apparatus of Dacey, Jr. relied on utilizing reference positions on the body-in-white, that resulted from imprecise and unknown locations due to the inherent stresses and distortions created during the assembly process, the positions were continuously different although within an acceptable tolerance range on each body-in-white. The datum position established based on these unknown distortions of the body-in-white created by the assembly and welding processes provided so called “design-intent” positions that varied significantly as a function of the inaccuracies of the vehicle frame created during assembly.
Akeel, U.S. Pat. No. 5,987,726, teaches a solution to avoid the creation of internal stresses that could cause failure of the assemblies when in use. Akeel teaches an apparatus for positioning an object during an assembly operation including a parallel link programmable positioning mechanism having a base plate, a spaced apart locator plate and six linear actuator links extending between the two plates and attached thereto by universal joints. The base plate is connected to the locator plate with the plurality of linear actuators, each having a lower end pivotably attached to the base plate and an upper end pivotably attached to the locator plate. When an object is mounted on the locator plate, the linear actuators are controlled to move the locator plate to a predetermined position relative to the base plate for contacting the object mounted on the locator plate with a component to be assembled. A feedback signal is generated representing a force supplied to the locator plate when the object contacts the component and thereafter the linear actuators are actuated to change the applied force in response to the feedback signal. This locating method provides for a stress free assembly of sheet metal components on assembly fixtures.
Kotake et al., U.S. Pat. No. 5,150,506, also teach a method of assembling exterior parts of an automobile wherein assembly accuracy errors of the vehicle body or body-in-white are determined by measuring the actual positions of a plurality of reference points of the body-in-white after it has been processed through the framing/welding station. Correction data is then generated by comparing the actual measured position of a point to the wire frame data or design-intent position of the same point while maintaining a correlated relationship amongst the parts, to eliminate correlated misalignment among those parts due to assembly accuracy errors of the body. The measurement of the assembled position of the vehicle body may be made at the assembly station of the parts or at any arbitrary station that is located on an upstream side of the assembly station. In the latter case, the measured as assembled data is read by a processor that generates correction data for the parts assembled positions that is transmitted from the measuring station to the assembling station. When the vehicle body is conveyed into the assembling station, the conveyed position is detected by encoders and the parts are assembled after corrections are made in accordance with the correction data. The reference points of the vehicle body are detected by the encoder device provided at the assembling station and, on the basis of the positional information, correction data for each assembling position of an exterior part is calculated by comparing the actual position detected by the encoders with the wire frame data in a computer so that the correction data is transmitted to a robot controller of a corresponding assembly robot to correct the assembling position of each part.
Accordingly, as desired, the location of any individual point on a panel after the body has been welded together is determined by the use of encoders and the deviation from the mean position of the point is calculated by comparing the actual reading to the net location of where that point should be so that a deviation from mean of the location of the point is determined. This deviation, in the form of a correction data, is communicated to the assembling robot in order to instruct the robot of the actual position of the point on the body-in-white panel with respect to the design-intent position so that each component to be assembled at that point may be separately adjusted to a corrected position in order to provide a corrected attachment point for assembling each of the outer body panels to the appropriate holes formed in the underbody and thereby maintain flushness of adjacent panels. Accordingly, each attachment point is selectively investigated as to deviation from mean and a correction is made when comparing the actual location of the attachment point to the mean location to ensure that the holes in the outer panels line up properly with the holes in the underbody to enable a successful attachment of the outer panel and ensure flushness to adjacent panels. Obviously, when using this sophisticated equipment in a production environment many problems can surface including but not limited to, environmental debris as a result of welding operations, sensitivity problems with the equipment, technical support team necessary to monitor equipment, etc. Also an additional station is needed in the production line to enable measurement by the encoders of the actual points on the body-in-white.
Therefore, what is needed is an apparatus and technique for assembling automotive frame components that recognizes and accepts the existence of these internal stresses and distortions of the various panels constituting the body-in-white that have been welded with, in some cases, as many as three thousand welds, yet is able to establish a reliable assembly technique utilizing a feature of Dacey, Jr., that is, insuring the fabrication of attachment points that are in a net or best fit position on the complete body-in-white that is also then assured to be in a known position so that the outer panels may be directly attached to the body-in-white with attachment points assured to be in the same position so that the outer panels may be directly attached to the body-in-white without the need for slip planes and without the need for being concerned of the inherent variations established by the body building process itself.